surface variations in phenolic plywood used as router table top
Hi Everyone,
I just built John White’s “Space-Saving Router Table” (FWW #216). I thought I would try phenolic plywood for the top, and purchased a sheet from a plywood specialty company just outside Boston MA. Hint of where this post is going: I asked where this plywood came from, and they said “far away.” But it wasn’t cheap, and it looked flat, so I pulled the trigger.
I built the table and assembled it face down on the granite countertop in my kitchen. I used a Veritas straightedge to verify kitchen countertop flatness to < 0.002″. I am recently divorced, so using the kitchen’s granite countertop as a reference surface is a new option for me! Sure enough, the router table top came out very flat. The problem became apparent when I leveled the BenchDog aluminum router plate within the table top: there are minor variations in the surface thickness of the phenolic so that when I level the corners of the router plate (i.e., make them absolutely flush with the surrounding table top), I can detect ridges protuding above the router plate on two sides. The ridge height is ~0.005″. That is enough to stop a board at the plate/top junction as I slide the board across the top. Even with the router installed, the BenchDog plate is flat to within my measuring precision. I can teeter a straightedge on the “bumps” in the top so I know it is the top and not the plate.
I have checked that the top is secured to the bottom frame (there are no gaps). So my questions are:
1) has anyone else had this problem?
2) how best to fix? I can probably sand down the bumps, but I might sand through the phenolic. Or I can adjust the router plate so it is a little proud of the top. I don’t yet have enough experience with router tables to know if a “proud plate” will cause problems.
Thanks in advance.
Replies
If it's rough I don't see a way around sanding it down - even if it doesn't snag a board edge I wouldn't want it adding scratches to any softer woods going over it. If you sand through it, perhaps it wasn't that good to begin with and you're better off adding a layer of high pressure laminate.
Just fine
I wish my table saw top was within ~.005 of flat, and my jointer, and planer, and bandsaw..... :)
Most stationary woodworking tool surfaces (at least the part where the wood goes) are not made with tolerances tighter than say .010", and even that is probably more accurate than necessary. My router table has the same issue, I just fiddled with the leveling screws until it worked good enough. If you can make the "in" side a little low and the "out" side a little high that may do the trick. You can also ease the edges of the router plate recess to help keep boards from catching.
Phenoic is more stable than say, CDX, but if something has wood fiber in it, it is going to move. Heck, the board you are runnning across the router table is probabaly changing a few thousands just from the heat of the bit.
Unless your slab has been re-machined it is not uniform in thickness nor particularly flat. Certainly acceptable for ordinary work, however. It iscertain that putting a window into substrate for a router lift will cause some distortion. If the framework you screw it down to is all in the same plane you can pull the deformity out of the slab. If the support is mishapen you'll produce some distortion in the slab. Notwithstanding, you can wet-sand the hi/lo spots out of phenolic, not a problem. No discontinuities from substrate to router lift plate? Rarely, and the reason this benchdog lift is under the MDF.
Try This
I would remove the router plate, turn the table upside down with the top on that granite and put some weights on the bhottom of the top. That buckle may well come out.
The prevent a reocurrance, I would releive the bottom corner of the opening ofr the router plate and make certain that the plate is not greating lateral pressure on the top.I might reinforce the cutout for teh router plate.
Dave
If you bought the light brown "phenolic" Plywood it is actually designed to line forms for concrete and does not neet to be very flat.
Try just raising your plate until it is flush or above the adjacent plywood. Make sure it is square to the router bit and have fun.
See Lee Valley /Veritas catalog for the router plate they sell that actually has a hump in it to assure that the table does not affect the cut.
Also, for fun, measure your other plywood in the shop. Once you get out to the thousanth decimal it varies wildly enven though it is smooth.
If you are like me and want things to be perfect only use fractions of an inch. 1/64 of an inch is 15 thou.
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